Plastic materials, such as polyesters, have been replacing glass and metal packaging materials due to their lighter weight, decreased breakage compared to glass, and potentially lower cost. One problem in this use of polyester for these applications is its relatively high gas permeability. This restricts the shelf life of carbonated soft drinks and oxygen sensitive materials such as beer and fruit juices. Organic oxygen scavenging materials for use in mixtures with plastic materials, such as polyesters, have been developed partly in response to the food industry's goal of having longer shelf-life for packaged materials.
One method of using oxygen scavenging materials which is currently being employed involves the use of “active packaging” where the package is modified in some way so as to control the exposure of the product to oxygen. One technique involves incorporating an oxygen scavenger into the package structure itself. In such a package structure, oxygen scavenging materials constitute at least a portion of the package. These materials remove oxygen from the enclosed package volume which surrounds the product or which may leak into the package, thereby inhibiting spoilage and prolonging freshness in the case of food products. Oxygen scavenging materials used in this package structure include low molecular-weight oligomers that are typically incorporated into polymers or oxidizable organic polymers in which either the backbone or side-chains of the polymer react with oxygen. A common oxidizable polymer used in a package structure is a polyamide, such as MXD-6 nylon. Such oxygen scavenging materials are typically employed with a suitable catalyst, for example an organic or inorganic salt of a transition metal catalyst such as cobalt.
U.S. Pat. No. 6,455,620 discloses polyethers, such as poly(alkylene oxide) glycols—for example polytetramethylene oxide glycol, as oxygen scavenging moieties blended with thermoplastic polymers and a transition metal catalyst. Typically copolyester-ethers are catalyzed by titanium alkoxide catalysts. The time required for the oxygen scavenging resin to begin scavenging oxygen once the package is formed is referred to as the “oxygen scavenging induction period”. The compositions taught in U.S. Pat. No. 6,455,620, when blended with polyesters, have a long oxygen scavenging induction period before scavenging oxygen in stretch blow molded containers.